NOx detection

Miura. N.. Zhuiykov, S., Takashi, H. and Yamazoe. N. (2002) Mixed potential type sensor using stabilized zirconia and ZnFe2O4 sensing electrode for NOx detection at high temperature. Sens. Actuators B, 83 (1-3), 222-9. 

N. and Oshima, T. (1998) O., detection using the electrolysis of water vapour in a YSZ cell. Part I. NOx detection. Solid State Ionics, 107, 213-16. 

Based on information about various oxides used for the SE in NO sensors given above, the new concept of potentiometric measurement of total NO regardless of the NO2 (NO) ratio in the exhaust gases at high temperatures has been developed recently [24, 34, 35]. In 1999, the ability to measure total NO in exhaust gases by a new zirconia-based laminated-type sensor was reported by Riken Corporation, Japan [34]. Since then, this sensor structure has been modified, and the new total-NOx detection system is shown conceptually in Figure 3.6 [35]. The main functions in this system are as follows ... 

The gases that the passenger of a car most needs to be protected from are CO and NOx detection of CO is considered to be the most important. 

For transportation industry applications, solid-state NOx sensing devices and materials operational at high temperatures are necessary [13-15]. While electrochemical sensors provide a promising approach for NOx detection in harsh environments, they can exhibit response to many different gases, thus minimizing selectivity. The two main components of nitrogen oxides in... 

A NOx gas sensor constructed from a molecularly-imprinted nitrate-selective electrode has also been developed in our laboratory (30). This gas sensor is produced by placing the nitrate-selective electrode behind a gas-permeable membrane. Also, there is a buffer compartment present between the gas-permeable membrane and the ISE. As before, NOx species that pass through the gas-permeable membrane are trapped in the buffer compartment as NO2 and NOs . In this case, the electrode responds proportionately to the amount of nitrate in the buffer, rather than nitrite as in the NOx sensor described above. The gas sensor based on the N03 -selective electrode offers advantages over the Severinghaus arrangement similarly to the other aforementioned gas sensors (SO2 and NOx). Detection limits for this gas sensor were on the order of 1x10 M, with response characteristics being retained for over 80 days. This lifetime is consistent with lifetimes of the molecularly-imprinted nitrate-selective electrodes. 

Closed symbols in Fig. 1 show the effect of reaction temperature on ammonia oxidation over CuO by heating with a conventional electric furnace. The reaction started at about 400 K and the conversion of NH3 became 1 at temperatures higher than 500 K. Fig. 1 also indicates that selectivity to N2 was high at low temperatures but it decreased as the temperature increased. Both N2O and NO increased instead of N2, except at 623 K, at which N2O decreases. NO was detected above 583 K, and it monotonously increased by the temperature. High reaction temperature seems to tend deeper oxidation to NOx. Considering that oxidation of N2 to N2O and NO is difficult in the tested temperature range. 

Water was produced through the reduction of stored NOx and was detected at the reactor exit with a time delay of about 50 s, that compared well with the characteristic time of C02desorption. Likewise, the consumption of C02 was ascribed to the reverse of reaction (10), which implied readsorption of C02 on BaO/Ba(OH)2 once NO had been reduced. 

The NOx concentrations are very low. Only for rigid polyurethane foam could NOx be detected before flashover, the value still too low to be specified. Recalculation of data through an estimation of average flow through the doorway just before flashover leads to typical values of 2 %, 8 % and 500 ppm for CO, C02 and (CH)n respectively for the materials studied. Both CO, C02 concentrations are reaching levels at which the gases have severe effects on humans and in the case of CO become lethal to man within one minute. 

The intrinsic sensors are based on the direct recognition of the chemicals by its intrinsic optical activity, such as absorption or fluorescence in the UV/Vis/IR region. In these cases, no extra chemical is needed to generate the analytical signal. The detection can be a traditional spectrometer or coupled with fiber optics in those regions. Sensors have been developed for the detection of CO, C02 NOx, S02, H2S, NH3, non-saturated hydrocarbons, as well as solvent vapors in air using IR or NIR absorptions, or for the detection of indicator concentrations in the UV/ Vis region and fluorophores such as quinine, fluorescein, etc. 

The NSR technology is regarded as the most reliable and attractive de-NOx method. However, catalyst degradation by SOx poisoning is a big problem. Sulfate was detected on the NSR catalyst after the aging test. S02 is oxidized and reacts with the NOx storage materials to form sulfates, which means the... 

Lindqvist subsequently described a similar system for the determination of HN03 (67). HN03 was collected on an Al2(S04)3-coated quartz denuder. The thermally desorbed NOx was determined by gas chromatogra-phy-photoionization detection. Subsequently Tanner et al. (68) simplified and fully automated the overall system configuration. A 51- X 0.4-cm quartz denuder tube was solution-coated with 20% w/v Al2(S04)3 and used at a very low Q (0.1 L/min). The desorption step involved heating to 500 °C for 1 min the liberated NOx was determined by a chemiluminescence monitor. Although laboratory results were attractive, field intercomparisons with a number of other methods indicated low and variable results the reasons for this discrepancy could not be identified with certainty. 

The observational program included getting information about the content and properties of atmospheric aerosol and most substantial optically active MGCs (03, CO, NOx, S02, etc.), but concentrated on aerosol studies to retrieve data on direct and indirect aerosol RF (ARF). The most interesting (and in many respects unexpected) results were connected with detection of a thick aerosol layer in the troposphere (an important feature of aerosol chemical composition consisted in the presence of a considerable black carbon component) and distinct manifestations of the long-range transport of both aerosol and MGCs. 

Akimoto and coworkers detected S2 following 248 nm photolysis of DMDS, implying that CH3 radicals are also produced (22). Low levels of CH3O2 and H02 radicals that could be produced in the C.W. experiments would not be removed by reactions with NOx but rather sustain a chain process leading to S02production. 

Tests were also performed on a Minnesota boiler equipped with a multicyclone and scrubber that normally burned a combination of coal, tree bark, and sludge (58). The measurements made by Pace Laboratories showed that with 15 percent tdf the particulate level rose to 0.09 pound per million Btu, compared to 0.05 pound per million Btu without tdf. The levels of S02 and NOx showed smaller increases, and polynuclear aromatic hydrocarbons were below detectable levels. 

Tsuda, T., Aoki, M., Kojima, M., Fujita, T. (1993) Accumulation and excretion of chloroanilines by carp. Chemosphere 26, 2301-2306. Tuazon, E.C., Winer, A.M., Pitts, J.N., Jr. (1978) Fourier transform infrared detection of nitroamines in irradiated amine-NOx systems. 

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